Various electronic measuring devices, such as calipers, micrometers, or gauges, are known that use electronic position encoders. These encoders are generally based on low-power inductive, capacitive, or magnetic position-sensing technology. In general, an encoder may comprise a readhead and a scale. The readhead may generally comprise a readhead sensor and readhead electronics. The readhead outputs signals that vary as a function of the position of the readhead sensor relative to the scale, along a measuring axis. In a measuring device such as an electronic caliper, the scale is generally affixed to an elongated scale member that includes a first measuring jaw and the readhead is affixed to a slider that is movable along the scale member and that includes a second measuring jaw. Thus, measurements of the distance between the two measuring jaws may be determined based on the signals from the readhead. Exemplary electronic calipers are disclosed in commonly assigned U.S. Pat. Nos. RE37490; 5,574,381; 5,973,494; 6,671,976; and 8,131,896, each of which is hereby incorporated by reference in its entirety.
Such electronic metrology tool devices may perform high-precision measurement operations, and calibration and/or certification operations may be performed on the devices to ensure the accuracy of the measurements. Once a device is calibrated, the calibration may be certified as being valid for a limited period of time or usage. For example, for a given calibration of a device, a due date may be determined when the calibration will expire and when recalibration will be required. In accordance with certain calibration standards, it may be desirable to limit the use of the device once the calibration has expired and until recalibration has been performed.
As one example, calibration may comprise checking the measurements provided by a device under specified test conditions (e.g., within a specified temperature range) against a standard or reference object that has a certified characteristic that is traceable back to a standard such as a length or dimension standard maintained at national laboratory, or a comparison or transfer standard established at a factory, or the like. If the measurements are within the specified accuracy of the device in comparison to the known characteristic of the standard, then the device may be considered “calibrated,” and may be certified as calibrated. Calibration need not necessarily comprise adjusting a device mechanically or electronically, or changing an internal scale factor or lookup table, or the like, although it may include such operations if they are needed to make the device perform within the specified accuracy.
One known technique for keeping track of calibration expiration dates is to put the relevant calibration information on a label that is attached to the device. U.S. Pat. No. 6,337,836 discloses a programmable electronic label that can be attached to a device and can track a calibration due date and provide an alert message when recalibration is required. However, a user may not see or may choose to ignore the label and continue to use the device for functions such as providing measurement data to a host device after the calibration has expired. Certain more complex devices may have the capacity to be programmed internally with calibration information; however, simpler devices such as already existing electronic calipers, micrometers, or gauges may lack the ability to be programmed in such a manner. A need exists for a system and method to track a limited calibration period for an existing measuring device such as an electronic caliper or micrometer or gauge, and to take action for inhibiting or altering the output of the device once the calibration period has expired.